Charge forming device or carburetor



Jail. 12, 1954 A J VQLZ ET AL 2,665,671

CHARGE FORMING DEVICE OR CARBURETOR Filed March 51, 1948 5 Sheets-Sheet l Azrnuz J. V: BY Hnvzv G. 72:71:

ATTORNEY 1954 A. J; VOLZ ET AL CHARGE FORMING DEVICE OR CARBURETOR 3 Sheets-Sheet 2 Filed March 51, 1948 INVENTORS Az'rnun J. Wu BY Heuzv 6.72211:

ATTORNEY Jan. 12, 1954 VQLZ ET AL 2,665,671

CHARGE FORMING DEVICE OR CARBURETOR Filed March 31, 1948 5 Sheets-Sheet I5 MAN/FOLD P125155.

MA N/FOLD TEMP? I //z' w 74 V (Ill/Illf/(Jgllll INVENTORS Aernu: J. VOLZ BY Hcmv G- 7:127:42

' ATTORNEY Patented Jan. 12, 1954 CHARGE FORMING DEVICE OR CARBURETOR Arthur J. Volz and Henry G. Tarter, South Bend, Ind., assignors to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Application March 31, 1948, Serial No. 18,188

15 Claims. 1

This invention relates to improvements in charge forming devices or carburetors for engines.

It has heretofore been proposed to. incorporate in fuel feeding systems for engines, particularly aircraft engines, means which tend to prevent or reduce the tendency towards detonation by enriching the fuel-air mixture as a function of Tmanifold. pressure and temperature when the engine is subjected to extremely heavy loads, as for example, during take-off and emergency power settings. Such devices, however, have lacked the necessary accuracy for maximum economy, have been difficult to adjust and for engines of certain characteristics the temperature response may be so slow as to result in too lean a mixture at the beginning of acceleration in the high power range.

An object of the present invention, therefore, is to provide in a carburetoror fuel metering device improved means for automatically producing enrichment of the fuel-air mixture as a functlonof manifold pressure and temperature. More specifically, the invention aims to provide in a fuel feeding system for engines metering means responsive to manifold pressure and temperature having improved characteristics with respect to accuracy, facility of adjustment and overcoming temperature lag.

Another object is to provide in a force feed or injection carburetor automatically operative manifold pressure and temperature responsive enrichment devices which may be readily adapted to the normal metering system.

The foregoing and other objects and advantages will become apparent in view of the following description taken in conjunction with the drawings, wherein:

Figure 1 is a schematic in section and elevation of an injection carburetor constructed in accordance. with thev present invention;

Figure 2 is an enlarged sectional schematic of the fuel control body portion of. the carburetor; and

Figure 3 is a fragmentary view of part of the controlsection of the carburetor, showing a modification in structure.

Referring to the drawings, a main air' intake conduit [3 leads to the supercharger H of an internal. combustion engine generally indicated at 2. The conduit ID. is controlled, by a pair of throttles l3. operable from the pilots cockpit in a known manner, and anterior the.- throttles is the carburetor i! including a large venturi l4 and a pair of boost venturis l5, ,In the type of fuel supply system used to illustrate the present invention, the pilot controls the air supply by manipulating the throttles I3, while the: metered liquid fuel is discharged under pressure into a supercharger slinger ring by means of a fuel discharge nozzle generally indicated: at t6. It will be understood, however, that the nozzle I6, instead of discharging into the air intake system in the manner shown, could be a series: of nozzles discharging directly into the individual engine cylinders as in the case of direct injection fuel feeding systems, or the nozzle could constitute part of a pressure feed system fora gas turbine or any other type of power plant towhich it may be adapted.

The fuel metering apparatus or carburetor I1 comprises two main sections, namely a fuel regulater section generally indicated at 18 and a fuel control body or section indicated at It. The regulator section or unit comprises a fuel valve 2| shown as of the poppet type and" arranged to slide in a valve body 22 mounted in a supporting boss 23 and formed with a series of inlet ports 24. Fuel is supplied to the ports 24 by way of a conduit 25, float chamber 26, strainer 21, strainer chamber 28 and conduit 29. The fuel ispreferably maintained under a substantially constant pressure, for example 17 p. s. i., by means such as a conventional fuel pump, not shown. The poppet valve 2| is carried by an air diaphragm 30 and a fuel diaphragm 3 I, which have their respective outer edges clamped between adjacent housing sections and their central portions clamped between a series of bushings removably secured on the stem 32 of the poppet valve 21. These diaphragms, together with a rigid parti tion 33 and a central sealing diaphragm 34, divide the interior of the regulator 18 at this point into a series of chambers, viz. air differential chambers A and B, and fuel differential chambers C and D. Chamber A is subjected to a measure of carburetor air intake pressure by means of a series of impact tubes 36, which have their entrance or intake ends located adjacent the carburetor deck and communicate with chamber A by way of annular chamber 31, valve port 38 and passage 39. Chamber B is subjected to Venturi suction by means of an annular channel, or chamber 40 formed. around the throat. of each of the small. or boost venturis l5, passage 41 and branchpassages 42, 42. Chambers C and D are subjected respectively to metered. and unmeteredfuel pressure. The small diaphragms 43 and 43 serve the purpose of balancing the regulator system including the poppet valve 2|. the

diaphragm 43 constituting the movable wall of a chamber 44 to which unmetered fuel under pressure is communicated by way of restricted channel 45. Another channel 46 serves to communicate accelerator pump fuel pressure to chamber 44 from accelerator pump 41, so that when the throttles I3 are suddenly opened, the pressure in chamber 44 is increased and the poppet valve 2| moved toward open position to increase the head across the metering jets for acceleration purposes.

The air chambers A and B are interconnected across the diaphragm 39 by a small passage 59 having bleeds 50' therein; and port 38 in the air passage 39 is varied as a function of altitude or changes in density by a valve 5! operatively connected to the movable end of a sealed corrugated bellows 52 which is mounted in a housing 53 open to the air intake conduit I Ii. The bellows 52 is loaded in a manner such as to render it responsive to changes in both pressure and temperature (see Patent No. 2,376,711 to Frank C. Mock), and is, therefore, responsive to changes in density. At relatively high barometric pressures, as for example, those prevailing at sea level, the bellows tends to collapse, causing valve 5| to increase the area of port 38, and increase the flow of air through passage 39, while at relatively low barometric pressures, as for example, those prevailing at high altitudes, the bellows tends to expand and cause the valve 5| to decrease the area of the port 38 and restrict the flow of air through the passage 39. As the passage 39 becomes more and more restricted, the differential across the air diaphragm is reduced, tending to reduce travel of the poppet valve 2! for a given change in throttle position. By this means the fuel-air ratio is maintained at a predetermined value irrespective of changes in altitude.

The particular construction of the regulator section of the carburetor forms no part of the present invention; it is shown for the purpose of presenting in combination with the control section of the carburetor a self-supporting disclosure.

The fuel control section I9 of the carburetor contains the metering jets and coacting control valves, and it is in this part of the carburetor that the improved manifold pressure and temperature responsive devices of the present invention are located.

Unmetered fuel from chamber D of the regulator section flows to the control section by way of a passage 69. In the diagrammatic or schematic illustration of Figure 2, this passage 66 has branches 6| and 62 leading therefrom. The branch BI contains a metering jet 63, commonly termed the automatic lean metering jet since this jet meters a relatively lean fuel-air mixture particularly adapted for low power settings. Beyond the jet 63, the branch passage 6| opens into a chamber or passage 64, from which fuel flows through port 65 controlled by a manual mixture control valve 66 into chamber 61 and thence by way of metered fuel conduit 63 to the discharge nozzle I6. The manual mixture control valve is provided with a handle or lever 66' which may be suitably controlled from the pilots compartment; it also includes a ported, disc-shaped, rotatable valve member 66" which in addition to the port 65, is formed with a port 69 adapted to selectively communicate a flow passage 10 with the chamber 61. In this passage 10 is another metering jet I0, commonly termed the autorich jet since when the flow through this jet is added to that through jet 63, the fuel-air ratio becomes sufficiently rich for most normal cruise conditions.

The fuel flowing through branch passage 52 may flow through either one or both parallel passages II or I2 and ports TI and 83 (which latter are controlled by separate pressure and temperature responsive valves I9 and 85), and thence by way of passage 13, port 14, chamber 15, passage 19, chamber 64, port 65 and conduit 68 to the discharge nozzle I6.

Valve port TI is defined by a seat member 78 and is controlled by contoured needle valve 19 connected to the movable end of a pressure responsive element such as bellows 80 located in a chamber 8|, to which manifold pressure may be communicated by way of a passage or conduit 82.

Valve port 83 is defined by a seat 84 and is controlled by contoured needle valve 85 having a stem slidingly mounted in a guide 66. This valve 85 is controlled primarily by a temperature responsive element such as a bellows 81 located in a chamber 88 and loaded with a suitable fluid medium. A temperature element 89 is preferably positioned in the engine intake manifold. It may be of any suitable type; in the form herein illustrated it is operatively connected with the interior of the bellows 81 by way of a capillary tube 90. As will be understood, when the thermal element 89 becomes heated, the fluid in the line 90 and bellows 81 expands, thereby expanding the bellows. The movable end of said bellows is in. abutting engagement with a contact head 9|: formed on the end of the stem of valve 85, said. stem being encircled by a spring 92 which engages a thrust collar 93 secured on said stem, so that the valve 85 is normally biased towards closed position and is opened in response to expansion movement of the bellows 81.

In order to insure prompt response of the temperature needle or valve 85 when the manifold pressure and temperature is suddenly increased, as by an opening movement of the throttles I3 and/or an increase in supercharger output, a socalled temperature anticipator generally indicated at 94 is provided; it comprises a diaphragm 94' having its central portion clamped or engaged between flanged stiffening and guide plates 95 and 96 and its peripheral edge portion clamped between inner and outer casing sections 91 and 98, which together with said diaphragm define a pair of pressure chambers 99 and I110. The diaphragm 94' is operatively connected to the valve 85 by means of a rod IIII, link I02, lever I03 pivoted or fulcrumed at I04, and yoke or fork I05 formed on the lower end of said lever. A spring I06 normally urges the diaphragm 94 and interconnecting linkage in a direction permitting the spring 92 to close the valve 85.

Manifold pressure is communicated to the chamber 99 by way of chamber 8| and port I01, while at the same time manifold pressure may be also communicated to chamber If!!! by way of chamber BI and control bleed I 98.

It will be seen that when there is a sudden increase in manifold pressure in the chamber 8|, there will be a corresponding increase in the chamber 99, the result of which is to cause the diaphragm 94' to move to the left and suddenly open the valve 85 until the pressure equalizes in the chambers 99 and I 00 due to the action of the bleed I08, whereupon the diaphragm 94 will move back to its neutral position. By this time the temperature element 89 and associated bellows 81 will have stabilized and have become effective to control the valve 85. The length of time required for the diaphragm 94' to move back and the valve 8.51maybepredetermineit by the capacity: of thecontrol. bleed I08, which ismadc a. function or the rate of response. of the tempera.- ture, control. adjustable contact I09; limits the maximum travel oflever I03 in, a valveopcningdirection.

The port 14 is defined by a. valve seat III in which an enrichment control valve H2 is mounted, said valve being provided with a stem H2 encircled by a spring H3 adaptedto n01?- mally urge or bias the valve towards closed position. This valve H2 is controlled by diaphragm I I5 clamped at itscentral portion between a pair of flanged stiffening and guide plates. H6 and I I1, the said. diaphragm in conjunction with. the surrounding walls defining chambers and II.8.. Unmetered fuel under pressure is communicated to: the chamber H8 by way of passage: H9, and when the metering head as determined: by" the pressure of the unmetercd fuel reaches a predetermined value, the valve H2 opens and permits fuel to flow from passage I3 to passage l6 and thence to the discharge nozzle It by way of chamber 54, port 65 and passage 68. Since the metering head varies in direct relation to the flow of air through the carburetor, the valve. H2; may be set to open only when the air flow attains a predetermined value. Since the valve I I2 is in series with the valves [9 and 84, it determinesthe point of enrichment on the power curve as a func tion, of mass flow of air through the carburetor; it prevents an over-rich mixture in case of low air flows and relatively high manifold pressures which prevail during certain operating conditions, as for example, where during cruising the engine propeller is set at a high pitch with the throttles wide open and which will increase the load on the engine so that it. slows down, whereupon. there is a low drop across the carburetor with a relatively high supercharger output.

A power enrichment jet I is located in passage 62.; it has a flow capacity sufficient to handle maximum enrichment flows.

An idle valve is indicated at. I.2I it controls a port I22 and. is connected by suitable linkage in a known manner to the throttles I3 to be. operated when the latter are initially opened and meter idling fuel. When the idle valve reaches a fully open position, metering is taken. over by the re spective metering jets in accordance with the position of the mixture control valve 66.

The valve indicated at I23, is a so-callcd fill.

valve; its purpose is to allow chamber C of the regulator to fill with fuel when the carburetor has been empty. It is held open in all manual mix:- ture control positions of valve 66 except idle cut-off by a cam on the inner end of the valve shaft.

The valve indicated at I25 is a derichment. valve for use when an antidetonant. system. is operatively associated with the carburetor; it controls flow of fuel to and through. a derichment jet- I26.

The passage indicated at I21 is for venting; chamber 0' of'the regulator to the discharge conduit 68.

Operation When the engine is running; air is drawn into the, air intake conduit I0. and through thesmall or boost venturis I5 and. main venturi It, and a difierential pressure is created between the throats of the small venturis, and the air; intake" which at constant, entering density propor-- tional to the square of the quantity of. air flowing;

These respective pressures, are transmitted to beingytcrmed the. air metering force.

6; chambers AandBcr the fuel regulator unit. on.

opposite sidesor. the air diaphragm it and create a net: force:- on. said diaphragm tending to. open.

the fuel or poppet valve. 2i, this. force usually If this. force were unopposed, the fuel or p ppet valve 2I would tend to move to full open position; but when the valveopens'. fuel under pressure flows into unmetered fuel chamber D and through eonduit. to. the. fuel. control section or body, where it flows through any one or more of the respective metering orifices. depending upon the position of. the manual control valve 6.6, and thence to the discharge. conduit 68. and discharge nozzle I51. from which itai's. discharged. under pressure into the airstream flowing to the engine. Chambcr D is: subjected to. unmctered fuel. pressure and chamber C tolmctered fuel pressure, and the dif ferential. between these. respective pressures acts on the diaphragm 3i, tending. to; move the poppet valve 21I to the left or-ina direction to close the. valve. This force is; commonly termed the fuel metering force and it opposes the air metering force. The valve 21 is: thus: caused to adjust I itself to a. point, of equilibrium such. that the. differential pressure across the fuel metering orifices, or. the metering head, is equal to the diiierential between. the air inlet. and the venturi. and in this manner, substantially constant fuel.- air proportioning is maintained. As engine speed is decreased, the rate of air flowing through the venturis is decreased, thereby decreasing the differential pressure. acting on. the diaphragm 25, causing the valve ZI to move towards closed position and decrease the fuelflow to compensate for decreased air flow. Since the venturi-to-air scoop. difierential. pressure increases upon a de.- crease in entering; air density, the differential pressure across the diaphragm 30 will tend to increase; thereby increasing, the fuel flow and enriching; the fuel mixture upon. a gain. in. altitude; The automatic control unit. including thebellows 52, coacts; withthe. calibrated bleed 50 to prevent such enrichment, said bleed bein substantiallyinefiective to vary;- the di-iferential pressure in chambers A. andB and across the air diaphragm 3.0.: at: suelt times when the needle valve 51-. is in, open; position, as at ground level, but becoming increasingly efiective in reducing the difierentialpressure as said needle progres sively restricts: the. port 3& and consequently the passage 39 with increase. in altitude. Thus, for any given mass air how, the needle 5| will so restrict the passage 39 with variations in altitude thatthe; diilierential pressure; inchambers A and B will remain constant. notwithstanding the fact that. the differential. in pressure at the venturis I5- and the impact. tubes 36 increases with a decrease in; entering air. density.

Coming now tot-the operation of the improved maniiold; pressure; and. temperature. responsive devices of: the-present. invention, let'it be. assumed that. the. manna-1: mixture. control valve 56 has beena turned. to a, position. where fuel may flow to the dischargenozzle. IiB through: the passages or channels. 812,10 and. 16 (which would be the position shown inli'igureizwhereboth ports and 69 are openli. Under" these: conditions, should the engine. power control lever (not shown) be advanced. to. a. point'where, for example; take o-ff power. is attained and. which; would necessitate a relatively-highcnginespeed at the usual propeller pitch setting; then ('1') the metering head would immediately increase to" a. value such that the fuel pressure in chamber H8 acting on the diaphragm I I would cause'thei vfalvei I2 to ripen; (2) the. build-up in manifold pressure would be communicated to the chamber fiI, causing the bellows 80 to collapse and open the valve I9; (3) this manifold pressure in chamber 8| would ii mediately be communicated to chamber 99 where it would act on the diaphragm err, tending to move the latter to the left, opening the temperature needle valve 85 to a predetermined metering position as determined by control bleed Hi3 and holding. the said valve open until the pressure entering through the control bleed IE8 equalized the pressure in the chambers 99 and It, and (4) there would be an increase in manifold temperature which would cause the bellows B7 to expand so that by the time the anticipator diaphragm 94 had released the valve 85, the temperature element 89 and bellows 81 would have stabilized and have taken over the metering control of valve 85. The function of the enrichment valve H2 and that of the manifold pressure valve I9 overlap to a certain extent. Thus, the valve I I2 meters as a function of mass flow of air to the engine as registered in the carburetor Venturi system and transmitted to the enrichment valve diaphragm I I5 in terms of fuel metering head, and under certain operating conditions this is a substantially true index of manifold pressure. However, this is not the case under all operating conditions, since factors such as propeller pitch, throttle position and altitude may produce a drop across the carburetor which could not be used as an index of manifold pressure. Furthermore, when the valve II2 is used alone, it must take care of such a wide range of manifold pressures and temperatures as to make it extremely diflicu t to set the valve so that it will give the most economical or best power mixture in all ranges, and the net result must be a compromise. By utilizing the valve H2 in series with parallel pressure and temperature controls, it will prevent enrichment at manifold pressures which are relatively high and yet not dangerously so, while at the same time the flow through the carburetor is relatively low. Invariably, when dangerous manifold pressures and temperatures are approached, the metering head has risen sufficiently to insure opening of valve II2. Once this valve opens, enrichment becomes a function of manifold pressure and temperature and may be accurately regulated since there are separate'or individual pressure and temperature controls.

Figure 3 In Figure 3, a modification is shown wherein a separate'manifold pressure valve "is dispensed with and a temperature responsive control is coordinated with the metering head valve I I2. In this instance, parts which are of identical construction with those shown in Figure 2 aregiven similar reference characters and'hence require no further explanation. 1 The temperature responsive bellows or element '81 in this'instance is provided with alink I30 at its'movable end which is pivotally connected at I3I to a lever I32, the latter at its upper end having a loose or shiftable pivotal connection by means of a slot I33 with the rod IIlI of the anticipator diaphragm 94'. At its opposite end, the-:lever I32 is operatively connected to the metering headgvalve I I2 by means of an adjustable contact I34 and-compression spring I35 of such strength or spring rate as will permit the valve'I I2- to open when the fuel metering head attains a predetermined value. g

8 If itbe assumed that the engine power control lever has been advanced to a setting calling for high take-off or emergency power, then the metering head or unmetered fuel pressure in chamber I I8 will attain a value such as will open the valve I I2 and permit fuel to flow from passage 82 and chamber 15 (heretofore described in connection with Figure 2) through port 14 to passage IIS, and thence by way of passage 84 of Figure 2, port 55 and passage or conduit 68 to the discharge nozzle IS of Figure 1. As the manifold pressure increases, there will be a corresponding increase in temperature, and immediately upon an increase in manifold pressure, the anticipator 94 becomes operative, the pressure in chamber 99 increasing and causing the diaphragm 94 to move to the left and relieve the pressure on spring I35, whereupon thevalve I I2 will further open to enrich the fuel mixture. The action of the anticipator will be only momentary, depending upon the capacity of the control bleed I88 and which is preferably chosen or calibrated as a function of the rate of response of the temperature bellows 87. Thus, as soon as the temperature element 89 and bellows 81 stabilize, the diaphragm 94' will move back and the temperature control will take over metering of the enrichment fuel. Since manifold temperature is a function of manifold pressure, and since also excessively high temperatures are conducive to detonation, an effective metering of enrichment fuel may be obtained.

Although only two embodiments of the invention have been illustrated and described, various changes in the form and relative arrangement of the parts may be made to suit requirements.

We claim:

1. In a fuel metering device for an engine having an intake manifold, fuel metering means adapted to maintain a predetermined normal ratio of fuel-to-air, independently operable valves arranged in parallel and adapted to meter supplementary fuel to the normal supply under high charge pressure and temperature conditions, an element responsive to changes in manifold pressure for controlling one of said valves and another element responsive to changes in manifold temperature for controlling the other of said valves.

2. In a fuel metering device for an engine having an air intake system including an intake manifold, fuel metering means for maintaining a-predetermined normal ratio of fuel-to-air, a pair of valves arranged in parallel for metering supplementary fuel to the normal supply under abnormally high charge pressure and temperature conditions, an element responsive to changes in manifold pressure for controlling one of said valves and another element responsive to changes in manifold temperature for controlling the other of said valves, a third valve arranged in series with said pressure and temperature valves for determining the point on the power curve at which said latter valves become effective to meter fuel to the normal supply, and means responsive to a function of the air intake system for controlling said third valve.

3. In a fuel metering device for an engine having an air intake system including an intake manifold, fuel metering means for maintaining a predetermined normal ratio of fuel-to-air in cluding a plurality of metering jets and means responsive to'changes in mass flow of air to the engine for establishing a metering head across said jets, a pair of independently operable valves formetering supplementary fuel to the engine iunder abnormally high charge pressure and temperature conditions, a. flexible element re- 1 sponsive to icha'ngesin intake manifold pressure I, for controlling one of said valves and another fuel control valve, means responsive to changes in temperature of the "air flowing to the engine for controlling said valve, means responsive to changes in anengine condition operatively connected to said valve and arranged to initially move said valve toward open position to avoid delay due to lag in temperature response of said first-named means, and means rendering said condition-responsive means ineffective immediately following initiation of valve opening movement.

5. In a fuel metering system for an engine, a fuel control valve, means responsive to changes in temperature of the air flowing to the engine for controlling said valve, means responsive to changes in the rate of flow of the air flowing to the engine adapted to initially move said valve toward open position prior to said temperature responsive means becoming effective to control the valve, and means rendering said secondnamed means ineffective to control said valve upon said temperature responsive means becoming effective to control the valve.

6. In a fuel metering system for an engine, a valve, pressure responsive means for controlling said valve, means responsive to change in temperature of the air flowing to the engine for actuating said valve, means responsive to changes in an engine condition adapted to initially act on said pressure responsive means when the englue is accelerated and move the valve toward open position to avoid lag due to delay in temperature response, and means for rendering said condition-responsive means ineffective to act on said pressureresponsive means immediately following opening movement of said valve.

'7. In a fuel metering system for an engine provided with a power control device, a valve, a pressure responsive element connected to said valve for controlling the latter, mean responsive to changes in temperature of the air flowing to the engine for controlling said valve, means defining a pair of pressure chambers on opposite sides of said element, means becoming effective upon an increase in power for automatically establishing a differential pressure across said element in a direction tending to open the valve, and means for automatically nullifying said differential when said temperature responsive means becomes effective to properly locate said valve.

8. In a system as claimed in claim 7, wherein said last named means includes a control bleed calibrated to determine the period of time over which said differential remains effective to control said valve.

9. In a fuel metering system for an engine pro vided with a power control device, a fuel control valve, means responsive to changes in temperature of the air flowing to the engine for controlling said valve, a pressure responsive element connected to said valve. means becoming effec- .tive uponan increase in powerfor subjecting said element to a differential pressure as a function of the rate of change of flow of the air flowing to the engine for initially moving said valve toward open position to avoid lag due to delay .in temperature response, and means for automatically determining the period of time over which said differential remains effective.

10. In a system as claimed in claim 9, wherein said pressure responsive element comprises a diaphragm and means defining a pair of pressure chambers on opposite sides of the diaphragm, and means for automatically subjecting said chambers to engine manifold differential pressures upon an increase in power to cause the diaphragm to act on said valve in a direction tending to open the latter. a.

.1'1. Ina pressure feed carburetor having fuel regulator and control sections, said control section being provided with a plurality of metering jets including a power enrichment jet and said regulator section being provided with a fuel control valve and means responsive to a differential pressure varying with the mass flow of air and fuel to the engine for controlling said valve to maintain a metering head across said jets, a pair of valves arranged in parallel in said control section for enriching the normal fuel mixture under high manifold pressure and temperature conditions, an element responsive to changes in manifold pressure for controlling one of said parallel valves and another element responsive to changes in manifold temperature for controlling the other of said parallel valves, a power enrichment valve arranged in series with said parallel pressure and temperature valves for determining the point on the power curve at which said latter valves become effective to enrich the normal fuel charge, and means responsive to the metering head for controlling said power enrichment valve.

12. In a fuel metering device for an engine having an air intake system including an intake manifold, fuel metering means including one or more metering jets and means operating as a function of the flow of air and fuel to the engine for maintaining a metering head across said jets, a power enrichment valve for enriching the normal fuel charge at a predetermined point in the power curve, means operating as a function of the flow of air to the engine for controlling said power enrichment valve, and means responsive to changes in manifold temperature arranged to control said power enrichment valve in conjunction with said first-named control means.

13. In a fuel metering device for an engine having an air intake system including an intake manifold, fuel metering means including a, plurality of metering jets, mean for maintaining a metering head across said jets as a function of the mass flow of air and fuel to the engine, a power enrichment valve, means responsive to the metering head for controlling said latter valve, means responsive to changes in engine manifold temperature also connected to said power enrichment valve for controlling the latter, and means responsive to the rate of change in manifold pressure for modifying the action of said temperature control.

14. In a fuel metering device for an engine having an air intake system including an intake manifold, fuel metering means including a plurality of metering jets, means for maintaining a metering head across said jets as a function of the mass flow of air and fuel to the engine, a power enrichment valve, means responsive to the metering head arranged to open said valve when the metering head attains a predetermined value, a temperature responsive element also operatively connected to said valve and arranged to modify the action of the latter as a function of manifold temperature, and means responsive to the rate of change in manifold pressure operatively connected to said enrichment valve and arranged to momentarily move the latter toward open position upon an increase in manifold pressure to avoid delay due to lag in temperature response.

15. In a fuel metering device for an engine, a fuel enrichment valve, means responsive to changes in engine manifold temperature having an operative connection with said valve, and means responsive to a differential pressure de- References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,136,959 Winfield Nov. 15, 1938 2,378,036 Reggie June 12, 1945 2,419,171 Simpson et a1. Apr. 15, 1947 2,428,377 Morris Oct. 7, 1947 2,440,241 Armstrong Apr. 27, 1948 2,536,888 Rabezzana Jan. 2, 1951 

